The present invention is a moisture curing composition comprising (a) an oxyalkylene polymer having at least one reactive silicon group in each molecule, (b) bis(3-triethoxysilylpropyl)tetrasulfane, and (c) a condensation catalyst. The presence of the bis(3-triethoxysilylpropyl)tetrasulfane in the composition provides for improved physical properties such as tensile strength and elongation. The present compositions are suitable for use in such applications as sealing materials for construction both in the form of extrudable liquid compositions and as cured preformed configurations such as tapes.
Typical moisture curable polymers include curable polyorganosiloxanes having a polyorganosiloxane backbone and at least one reactive silicon group which reacts with moisture to form siloxane bonds. However, such curable polyorganosiloxanes have several limitation including their expense and lack of paintability. Oxyalkylene polymers having reactive silicone groups that are crosslinkable in the presence of moisture to form siloxane bonds have been proposed as an alternative to such curable polyorganosiloxane compositions. Although such oxyalkylene polymer containing compositions overcome at least partially the above described limitations of the polyorganosiloxane compositions, they could still benefit from improve properties such as tensile and elongation.
Isayama et al., U.S. Pat. No. 3,971,751, describe methods for making polyether polymers having reactive silicon groups and compositions comprising these polymers which are curable to a rubber-like substance upon exposure to moisture.
Takago et al., U.S. Pat. No. 4,323,488, describe a method for making allyl-terminated polyoxyalkylene polyethers and curable compositions containing such polymers.
Kawakubo et al., U.S. Pat. No. 4,788,254, describe a moisture curable polymer composition comprising (a) an organic polymer having at least one reactive silicon group in a molecule and (b) a compound having one silanol group in a molecule or a compound which reacts with moisture to form a compound having one silanol group in a molecule. The composition is reported to have improved tensile strength and surface characteristics.
Kawakubo et al., U.S. Pat. No. 4,837,274, describe a curable composition comprising an organic polymer containing at least one reactive silicon functional group crosslinkable to produce an elastomer by the formation of a siloxane bond and an organosilicon compound having a molecular weight of not less than 140. The cured composition is reported to having excellent modulus, elongation, and storage stability.
Yukimato et al., U.S. Pat. No. 4,983,700, describe a curable composition comprising an (a) oxyalkylene base polymer having at least one reactive silicon-containing group bonded to a silicon atom, (b) at least one compound selected from the group consisting of a compound having one silanol group in the molecule and a compound which when reacted with moisture, generates a compound having one silanol group in the molecule, (c) a compound having a silicon-containing group to the silicon atom of which two hydrolyzable groups are bonded, and (d) a compound having a silicon-containing group to the silicon atom of which three hydrolyzable groups are bonded and an amino group, which composition provides a cured material having low modulus, good bond strength, and improved weather resistance of the bond strength.
Hasegawa et al., EP 0-620-241 A1, describe a curable composition comprising an oxyalkylene polymer having a silicon atom-containing group to which a hydroxyl group or a hydrolyzable group is bonded and capable of crosslinking to form a siloxane bond, and a hydrolyzable silicon compound. The addition of the hydrolyzable silicon compound is reported to improve adhesion of the cured compositions to substrates and markedly improved water-resistant adhesion.